This invention relates to the fracture separation, into a bearing cap and a connecting rod, of an integral preform, while ensuring that the separated pieces will be capable of reunification, in a high production environment.
Numerous methods have been employed to separate connecting rod preforms by fracturing, both in laboratory and production environments. These include cryogenic cooling or electron beam exposure to embrittle the fracture area, fracturing by wedge actuation of an expanding mandrel, and linear opposing pulling forces to separate the bearing cap from the connecting rod preform. The following patents are representative of the prior art:
U.S. Pat. No. 4,569,109, issued Feb. 11, 1986;
U.S. Pat. No. 4,768,694, issued Sep. 6, 1988;
U.S. Pat. No. 4,993,134, issued Feb. 19, 1991.
Despite these prior developments, certain elements vital to fracture separation continue to have the greatest influence on the quality of the finished connecting rod. Two of these elements are:
(1) achieving simultaneous fracture along the crackling plane of both legs of the connecting rod. Failure to achieve simultaneous fracture is likely to result in plastic deformation of the crank bore and inhibit remating of the two parts;
(b) maintaining positive control over the position of the separated bearing cap and connecting rod body, to ensure accurate micro-alignment during re-mating. Failure to do this may negate the inherent advantages of fracture separation.
The present invention provides an apparatus and a process for accomplishing the fracture separation, into a bearing cap and a connecting rod, of an integral preform, the latter being composed of powdered metal, cast iron, forged steel, aluminum or any other material suitable for use as a connecting rod. The process of this invention is conducted under ambient conditions and requires no prior embrittlement of the preform, as called for by earlier developments utilizing cryogenic chilling or electron beam hardening.
However, a stress-riser is required to control the location of fracture initiation (i.e. the location of the joint line). The stress-riser may be provided in a prior process by way of (a) V-notch broaching or other equivalent machining means, (b) laser etching, or (c) preforming a stress-riser in the xe2x80x9cgreenxe2x80x9d preform prior to firing (baking) and forging.
The present process utilizes a work-holding fixture which retains and locates the connecting rod preform with repspect to its manufacturing datum features. The mechanism includes a dual slide ram coupled to a unilateral wedge interposed between a two-piece mandrel which, when activated, effects the fracture separation of the preform into a bearing cap and the connecting rod.
A further aspect of this process is the ability of the work-holding fixture to locate the pre-separated connecting rod preform on the manufacturing datum features, and to maintain this location throughout separation and re-mating. This goal is achieved by constructing the work-holding feature on a precision slide. A lower portion of the work-holding fixture, which rigidly secures the connecting rod body, is affixed to the slide and restrains the connecting rod against any movement. The upper portion of the work-holding fixture, which locates and retains the bearing cap of the ultimate connecting rod, is affixed to a slide saddle movable on the precision slide.
This arrangement allows the bearing cap to move independently of the connecting rod body during separation, while continuing to maintain its precision location with respect to the connecting rod body. The arrangement of the present invention further eliminates any tendency for the bearing cap to rotate during separation, thus promoting simultaneous fracture of both of the connecting rod legs. The re-mating of the separated bearing cap to the connecting rod body is passively accomplished by spring loading the upper portion of the work-holding fixture to return it to its pre-fracture position. Subsequent to the fracture separation and re-mating of the bipartite connecting rod, the work-holding fixture, with is re-mated connecting rod still retained and located, can index out of the separation area for fastener insertion and further processing as required.
More particularly, this invention provides an apparatus for the fracture separation, into a bearing cap and a connecting rod, of an integral preform which is configured to define a cylindrical aperture and two spaced-apart bolt seat shoulders, the apparatus comprising:
a base member
a guide member fixed with respect to said base member, the guide member defining a first guideway extending in a first direction,
a first slide member mounted to said guide member for sliding movement along said first guideway in said first direction, the first slide member defining a second guideway also extending in said first direction,
a second slide member mounted to said first slide member for sliding movement with respect to said first slide member along said second guideway in said first direction,
a mandrel which is split to define an upper part fixed with respect to the first slide member and a lower part fixed with respect to said base member, said upper part being movable between a first position in which it is spaced away from the lower part and a second position in which it is juxtaposed against the lower part to define a substantially cylindrical body having its axis lying substantially in a second direction perpendicular to said first direction, movement of said upper part being simultaneous with movement of the first slide member along the first guideway with respect to said guide member, the upper and lower parts of said mandrel defining an internal tapered passageway,
a wedge member adapted, when the upper part is in its second position, to enter said tapered passageway and force said mandrel parts apart, power means for moving said wedge member, projections defined by said second slide member and adapted to contact the bolt seat shoulders of an integral preform while the cylindrical aperture thereof receives the split mandrel, and means for selectively urging the second slide member toward the mandrel, thereby securely holding the integral preform in place, whereby the wedge member can enter the tapered passageway, forcing the mandrel parts apart and fracturing the preform into a bearing cap and a connecting rod.
Further, this invention provides a process for the fracture separation, into a bearing cap and a connecting rod, of an integral preform which is configured to define a cylindrical aperture and two spaced-apart bolt seat shoulders, the process comprising:
a) fitting they cylindrical aperture of the preform over a substantially cylindrical mandrel which includes separate upper and lower parts,
b) holding the preform in place over the mandrel by pressing against the bolt seat shoulders in the direction toward the mandrel, and
c) forcing the mandrel parts apart while holding the preform in place, thereby to fracture the preform into a bearing cap and a connecting rod.